The present invention relates to gear pump and motor apparatus adapted to operate alternatively either as a pump or as a motor of the type which includes a pair of meshing gears whose shafts are respectively supported in a housing by separate bearing sleeves and whose inner faces sealingly engage the faces of the gears by means of oil pressure which urge the bearing sleeves in an axial direction so as to provide a tight sealing engagement.
With respect to the state of the art of such gear pump and motor apparatus, reference is made to British Pat. Publication No. 1,067,552 and German Application Publication (OS) No. 1,703,180.
Further regarding the state of the art, reference is also made to applicant's Finnish Pat. Nos. 51,992 and 51,993. The gear pump/motor disclosed in Finnish Pat. No. 51,992 includes features whereby tilting of the bearing sleeves under varying operating conditions is prevented. More particularly, in this gear pump/motor, the elevated pressure in the gear chamber is directed from an axial sleeve equilibrium field to partial pressure fields defined by sealing members through pressure compensating openings located in the bearing sleeves in the middle of the region where pressure increases during average operating conditions so that in this manner tilting of the bearing sleeves under conditions which deviate from the normal is eliminated.
It is of course necessary in gear pump/motor apparatus of the type described above to provide lubrication between the bearing sleeves and the shaft of the respective gear received therein. Generally, in conventional arrangements, such lubrication is accomplished through the application of a vacuum or by means of oil passages directed from the inlet side of the chamber into the bearing sleeves. However, such conventional arrangements are not entirely satisfactory when used in connection with a gear pump/motor which rotates in two directions since the passages must necessarily be located in an asymmetric fashion on the face surfaces of the bearing sleeves.
For maximum total efficiency, a texlon coating is provided on the inner face surface of each bearing sleeve which reduces oil leakage from the gear housing to the gear shaft located within the bearing sleeve.
Another arrangement has been suggested for providing a controlled oil leakage from the gear chamber to the gear shaft journal within the bearing sleeve. Thus, the curvature of the gear teeth directed towards the gear face has been increased in order to promote such oil leakage to facilitate lubrication. However, this technique has not proved satisfactory for a variety of reasons. More particularly, due to the difference in curvature in the gear teeth, the pressure unavoidably is distributed on the side of the gear teeth having the increased curvature. Thus, an uneven pressure distribution acts on the gears giving rise to a differential pressure which tends to move the gears against the opposing sleeve bearing resulting in a higher leakage at the end face of the gear facing the sides of the teeth having the increased curvature and the possibility of seizing of the bearing sleeve face at the side opposing the gear teeth having lesser curvature.
It has also been proposed in connection with providing a controlled leakage of oil from the gear pump/motor housing to the gear shaft journal to provide a groove in the central neck region of the face of the bearing sleeve so that oil leaking from the housing passes between the gear and face and the mating end face of the bearing sleeve. However, such arrangements have the disadvantage that the groove must be extremely small and as the face of the bearing sleeve wears during operation, the groove becomes filled with material which obstructs the flow of oil to the gear shaft journal.
Furthermore, difficulties have arisen in drilling bores or passages having a small diameter to the bearing sleeve from the pressure side of the pump/motor in order to provide a controlled leakage directly to the bearing sleeve. For example, in order to provide a suitable leakage flow, namely about 1 liter per minute, through a passage having a length of 18.5 mm, the bore necessarily requires a diameter of about 0.25 mm. Thus, the length/diameter ratio in this example is 74. However, in practice, it has been found that the highest recommended length/diameter ratio is about 10. Further, the location of such a passage or bore is unsatisfactory especially in connection with combination pump/motor arrangements which rotate in two directions wherein such a provision is not possible.